High-Fidelity, Frequency-Flexible Two-Qubit Fluxonium Gates with a Transmon Coupler

Abstract

We propose and demonstrate an architecture for fluxonium-fluxonium two-qubit gates mediated by transmon couplers (FTF, for fluxonium-transmon-fluxonium). Relative to architectures that exclusively rely on a direct coupling between fluxonium qubits, FTF enables stronger couplings for gates using non-computational states while simultaneously suppressing the static controlled-phase entangling rate ($ZZ$) down to kHz levels, all without requiring strict parameter matching. Here we implement FTF with a flux-tunable transmon coupler and demonstrate a microwave-activated controlled-Z (CZ) gate whose operation frequency can be tuned over a 2 GHz range, adding frequency allocation freedom for FTF's in larger systems. Across this range, state-of-the-art CZ gate fidelities were observed over many bias points and reproduced across the two devices characterized in this work. After optimizing both the operation frequency and the gate duration, we achieved peak CZ fidelities in the 99.85-99.9\% range. Finally, we implemented model-free reinforcement learning of the pulse parameters to boost the mean gate fidelity up to $99.922\pm 0.009\%$, averaged over roughly an hour between scheduled training runs. Beyond the microwave-activated CZ gate we present here, FTF can be applied to a variety of other fluxonium gate schemes to improve gate fidelities and passively reduce unwanted $ZZ$ interactions.

23 pages, 16 figures

References in corpus (16)

• Supplementary information for "Quantum supremacy using a programmable superconducting processor"
• Charge insensitive qubit design derived from the Cooper pair box
• Coupling Superconducting Qubits via a Cavity Bus
• Suppressing quantum errors by scaling a surface code logical qubit
• Simple pulses for elimination of leakage in weakly nonlinear qubits
• Robust randomized benchmarking of quantum processes
• Real-time quantum error correction beyond break-even
• Fidelity of quantum operations
• Process verification of two-qubit quantum gates by randomized benchmarking
• Fluxonium: an alternative qubit platform for high-fidelity operations
• Model-Free Quantum Control with Reinforcement Learning
• Deep Reinforcement Learning for Quantum Gate Control
• High fidelity two-qubit gates on fluxoniums using a tunable coupler
• Scalable High-Performance Fluxonium Quantum Processor
• Analytic Design of Accelerated Adiabatic Gates in Realistic Qubits: General Theory and Applications to Superconducting Circuits
• Fast and Robust Geometric Two-Qubit Gates for Superconducting Qubits and beyond

Cited by in corpus (66)

• Reducing leakage of single-qubit gates for superconducting quantum processors using analytical control pulse envelopes
• Realization of High-Fidelity CZ Gate based on a Double-Transmon Coupler
• Beyond NISQ: The Megaquop Machine
• Scalable, high-fidelity all-electronic control of trapped-ion qubits
• Robust Quantum Gates against Correlated Noise in Integrated Quantum Chips
• Blueprint for all-to-all connected superconducting spin qubits
• Native approach to controlled-Z gates in inductively coupled fluxonium qubits
• Experimental advances with the QICK (Quantum Instrumentation Control Kit) for superconducting quantum hardware
• Efficient initialization of fluxonium qubits based on auxiliary energy levels
• High coherence fluxonium manufactured with a wafer-scale uniformity process
• Cavity-mediated entanglement of parametrically driven spin qubits via sidebands
• Long-range-enhanced surface codes
• High-precision pulse calibration of tunable couplers for high-fidelity two-qubit gates in superconducting quantum processors
• Dynamic-ADAPT-QAOA: An algorithm with shallow and noise-resilient circuits
• Direct Implementation of High-Fidelity Three-Qubit Gates for Superconducting Processor with Tunable Couplers
• Comparative study of quantum error correction strategies for the heavy-hexagonal lattice
• Optimal control in large open quantum systems: the case of transmon readout and reset
• Gatemonium: A Voltage-Tunable Fluxonium
• A Review of Design Concerns in Superconducting Quantum Circuits
• One Gate Scheme to Rule Them All: Introducing a Complex Yet Reduced Instruction Set for Quantum Computing
• Layering and subpool exploration for adaptive Variational Quantum Eigensolvers: Reducing circuit depth, runtime, and susceptibility to noise
• Dephasing in Fluxonium Qubits from Coherent Quantum Phase Slips
• High-performance multiqubit system with double-transmon couplers: Toward scalable superconducting quantum computers
• Parametrically-controlled microwave-photonic interface for the fluxonium
• Flux-pulse-assisted Readout of a Fluxonium Qubit
• Designing fast quantum gates using optimal control with a reinforcement-learning ansatz
• Globally driven superconducting quantum computing architecture
• Characterization of drive-induced unwanted state transitions in superconducting circuits
• Impact of Josephson junction array modes on fluxonium readout
• The iSWAP gate with polar molecules: Robustness criteria for entangling operations
• Long-Range Four-body Interactions in Structured Nonlinear Photonic Waveguides
• An engineering guide to superconducting quantum circuit shielding
• All-thermal reversal of heat currents using qutrits
• Capacitively Shunted Double-Transmon Coupler Realizing Bias-Free Idling and High-Fidelity CZ Gate
• Sub-Harmonic Control of a Fluxonium Qubit via a Purcell-Protected Flux Line
• Verifying the analogy between transversely coupled spin-1/2 systems and inductively-coupled fluxoniums
• Single-Qubit Gates Beyond the Rotating-Wave Approximation for Strongly Anharmonic Low-Frequency Qubits
• Noise reduction via optimal control in a light-matter quantum system
• Fast microwave-driven two-qubit gates between fluxonium qubits with a transmon coupler
• Gatemon Qubit Revisited for Improved Reliability and Stability
• Above 99.9% Fidelity Single-Qubit Gates, Two-Qubit Gates, and Readout in a Single Superconducting Quantum Device
• Fermionic Quantum Simulation on Andreev Bound State Superlattices
• SuperGrad: a differentiable simulator for superconducting processors
• Cross-resonance control of an oscillator with an auxiliary fluxonium qubit
• GPU-accelerated Effective Hamiltonian Calculator
• Parameter optimization for the unimon qubit
• Viewing protected superconducting qubits through the lens of the cat qubit
• Theory of Multi-photon Processes for Applications in Quantum Control
• Scalable Low-overhead Superconducting Non-local Coupler with Exponentially Enhanced Connectivity
• Concurrent Fermionic Simulation Gate
• Efficient Eigenstate Preparation in an Integrable Model with Hilbert Space Fragmentation
• Non-demolition fluorescence readout and high-fidelity unconditional reset of a fluxonium qubit via dissipation engineering
• Effect of Etching Methods on Dielectric Losses in Transmons
• Simultaneous sweet-spot locking of gradiometric fluxonium qubits
• Flux-Trapping Fluxonium Qubit
• Performance-centric roadmap for building a superconducting quantum computer
• Overhead in Quantum Circuits with Time-Multiplexed Qubit Control
• Transmon-assisted high-fidelity controlled-Z gates for integer fluxonium qubits
• Optimizing the frequency positioning of tunable couplers in a circuit QED processor to mitigate spectator effects on quantum operations
• Low-rank optimal control of quantum devices
• Scalable phonon-laser arrays with self-organized synchronization
• The perfect entangler spectrum as a tool to analyze crosstalk
• Hybrid superinductance with Al/InAs
• Proposal for erasure conversion in integer fluxonium qubits
• Mitigating state transition errors during readout with a synchronized flux pulse
• A fluxonium qubit-based hybrid electromechanical system